All-wheel drive drivetrains for vehicles allow driving power to be delivered to all four wheels of the vehicle. By delivering driving power to all four wheels, vehicle performance is improved when surface conditions are poor. As examples, all-wheel drive systems can improve vehicle performance when road surfaces are slippery as a result of rain or snow, and when the road surface itself is of poor quality, such as dirt or gravel road surfaces.
In all wheel-drive vehicles with a transversely mounted front-engine layout, a transaxle is typically utilized to provide a desired gear ratio and to distribute driving power to the left and right front wheels by way of a front differential and a front axle. A power transfer unit receives driving power from the front axle and transfers driving power to the rear wheels of the vehicle by way of a driveshaft, a rear differential, and a rear axle. In some implementations, the power transfer unit is configured to disconnect the power transfer path to the rear wheels. Conventionally, the power transfer unit is sealed with respect to the transaxle because the fluids utilized are different. For instance, an automatic transaxle is typically operated by and lubricated with hydraulic fluid (i.e. automatic transmission fluid) while the power transfer unit is lubricated by gear oil that has a much higher viscosity than conventional hydraulic fluid. Thus, the actuation and fluid management systems of a conventional power transfer unit are separate from those of a conventional transmission.